Depends on what you are paying for things and a bit of luck. If you are working the room on ebay and other forums and buying of example low hour motors as they come up then you can do OK. If you start with $500 buck shitter that has done its time chasing cows then things will get expensive.
Usually start with good motor or frame as the rest you pitch usually anyway. Most expensive bike so far to build was my HL500 but it was built knowing it would really cost $$$ and owes less than some NOS TT500s I know.